The FBI’s Biometric Center of Excellence, which already collects tattoos and other identity markers in its massive database, sent a request July 13 to police agencies for information “related to any current databases containing tattoo/symbol images, their possible meanings, gang affiliations, terrorist groups or other criminal organizations.”

Gang members and terrorist groups often share symbols among their followers as a way to easily identify one another and gauge member loyalty. Members of the Latin Kings, for example, illustrate their bodies with a crown, while members of the MS-13 gang usually tattoo “MS” on their skin. But other symbols are more cryptic.

FBI agents say combining their database with information gathered from tattoo databases at more than 18,000 law enforcement agencies could improve everyone’s biometric-based crime-fighting and anti-terrorism efforts.

“Some of our database users have expressed a desire for (knowing) what tattoos may potentially mean,” said Bill Casey, the program director at the FBI’s biometric center. “We are trying to learn the lay of the land and see if there are any databases out there agencies may want to share.”